/*
 * tftp.c - a simple, read-only tftp server for qemu
 *
 * Copyright (c) 2004 Magnus Damm <damm@opensource.se>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "slirp/slirp.h"

#include <stdio.h>

struct tftp_session {
        int in_use;
        char filename[TFTP_FILENAME_MAX];

        struct in_addr client_ip;
        u_int16_t client_port;

        int timestamp;
};

struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];

const char *tftp_prefix;

static void tftp_session_update(struct tftp_session *spt) {
        spt->timestamp = curtime;
        spt->in_use = 1;
}

static void tftp_session_terminate(struct tftp_session *spt) { spt->in_use = 0; }

static int tftp_session_allocate(struct tftp_t *tp) {
        struct tftp_session *spt;
        int k;

        for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
                spt = &tftp_sessions[k];

                if (!spt->in_use)
                        goto found;

                /* sessions time out after 5 inactive seconds */
                if ((int)(curtime - spt->timestamp) > 5000)
                        goto found;
        }

        return -1;

found:
        memset(spt, 0, sizeof(*spt));
        memcpy(&spt->client_ip, &tp->ip.ip_src, sizeof(spt->client_ip));
        spt->client_port = tp->udp.uh_sport;

        tftp_session_update(spt);

        return k;
}

static int tftp_session_find(struct tftp_t *tp) {
        struct tftp_session *spt;
        int k;

        for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
                spt = &tftp_sessions[k];

                if (spt->in_use) {
                        if (!memcmp(&spt->client_ip, &tp->ip.ip_src, sizeof(spt->client_ip))) {
                                if (spt->client_port == tp->udp.uh_sport) {
                                        return k;
                                }
                        }
                }
        }

        return -1;
}

static int tftp_read_data(struct tftp_session *spt, u_int16_t block_nr, u_int8_t *buf, int len) {
        FILE* file;
        int bytes_read = 0;

        file = fopen(spt->filename, "rb");

        if (file == NULL) {
                return -1;
        }

        if (len) {
                fseek(file, block_nr * 512, SEEK_SET);

                bytes_read = fread(buf, len, 1, file);
        }

        fclose(file);

        return bytes_read;
}

static int tftp_send_error(struct tftp_session *spt, u_int16_t errorcode, const char *msg, struct tftp_t *recv_tp) {
        struct sockaddr_in saddr, daddr;
        struct SLIRPmbuf *m;
        struct tftp_t *tp;

        m = m_get();

        if (!m) {
                return -1;
        }

        memset(m->m_data, 0, m->m_size);

        m->m_data += if_maxlinkhdr;
        tp = (void *)m->m_data;
        m->m_data += sizeof(struct udpiphdr);

        tp->tp_op = htons(TFTP_ERROR);
        tp->x.tp_error.tp_error_code = htons(errorcode);
        strncpy((char *)tp->x.tp_error.tp_msg, msg, sizeof(tp->x.tp_error.tp_msg));
        tp->x.tp_error.tp_msg[sizeof(tp->x.tp_error.tp_msg) - 1] = 0;

        saddr.sin_addr = recv_tp->ip.ip_dst;
        saddr.sin_port = recv_tp->udp.uh_dport;

        daddr.sin_addr = spt->client_ip;
        daddr.sin_port = spt->client_port;

        m->m_len = sizeof(struct tftp_t) - 514 + 3 + strlen(msg) - sizeof(struct ip) - sizeof(struct udphdr);

        udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

        tftp_session_terminate(spt);

        return 0;
}

static int tftp_send_data(struct tftp_session *spt, u_int16_t block_nr, struct tftp_t *recv_tp) {
        struct sockaddr_in saddr, daddr;
        struct SLIRPmbuf *m;
        struct tftp_t *tp;
        int nobytes;

        if (block_nr < 1) {
                return -1;
        }

        m = m_get();

        if (!m) {
                return -1;
        }

        memset(m->m_data, 0, m->m_size);

        m->m_data += if_maxlinkhdr;
        tp = (void *)m->m_data;
        m->m_data += sizeof(struct udpiphdr);

        tp->tp_op = htons(TFTP_DATA);
        tp->x.tp_data.tp_block_nr = htons(block_nr);

        saddr.sin_addr = recv_tp->ip.ip_dst;
        saddr.sin_port = recv_tp->udp.uh_dport;

        daddr.sin_addr = spt->client_ip;
        daddr.sin_port = spt->client_port;

        nobytes = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);

        if (nobytes < 0) {
                m_free(m);

                /* send "file not found" error back */

                tftp_send_error(spt, 1, "File not found", tp);

                return -1;
        }

        m->m_len = sizeof(struct tftp_t) - (512 - nobytes) - sizeof(struct ip) - sizeof(struct udphdr);

        udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

        if (nobytes == 512) {
                tftp_session_update(spt);
        } else {
                tftp_session_terminate(spt);
        }

        return 0;
}

static void tftp_handle_rrq(struct tftp_t *tp, int pktlen) {
        struct tftp_session *spt;
        int s, k, n;
        u_int8_t *src, *dst;

        s = tftp_session_allocate(tp);

        if (s < 0) {
                return;
        }

        spt = &tftp_sessions[s];

        src = tp->x.tp_buf;
        dst = (u_int8_t *)spt->filename;
        n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);

        /* get name */

        for (k = 0; k < n; k++) {
                if (k < TFTP_FILENAME_MAX) {
                        dst[k] = src[k];
                } else {
                        return;
                }

                if (src[k] == '\0') {
                        break;
                }
        }

        if (k >= n) {
                return;
        }

        k++;

        /* check mode */
        if ((n - k) < 6) {
                return;
        }

        if (memcmp(&src[k], "octet\0", 6) != 0) {
                tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
                return;
        }

        /* do sanity checks on the filename */

        if ((spt->filename[0] != '/') || (spt->filename[strlen(spt->filename) - 1] == '/') || strstr(spt->filename, "/../")) {
                tftp_send_error(spt, 2, "Access violation", tp);
                return;
        }

        /* only allow exported prefixes */

        if (!tftp_prefix || (strncmp(spt->filename, tftp_prefix, strlen(tftp_prefix)) != 0)) {
                tftp_send_error(spt, 2, "Access violation", tp);
                return;
        }

        /* check if the file exists */

        if (tftp_read_data(spt, 0, (u_int8_t *)spt->filename, 0) < 0) {
                tftp_send_error(spt, 1, "File not found", tp);
                return;
        }

        tftp_send_data(spt, 1, tp);
}

static void tftp_handle_ack(struct tftp_t *tp, int pktlen) {
        int s;

        s = tftp_session_find(tp);

        if (s < 0) {
                return;
        }

        if (tftp_send_data(&tftp_sessions[s], ntohs(tp->x.tp_data.tp_block_nr) + 1, tp) < 0) {
                return;
        }
}

void tftp_input(struct SLIRPmbuf *m) {
        struct tftp_t *tp = (struct tftp_t *)m->m_data;

        switch (ntohs(tp->tp_op)) {
        case TFTP_RRQ:
                tftp_handle_rrq(tp, m->m_len);
                break;

        case TFTP_ACK:
                tftp_handle_ack(tp, m->m_len);
                break;
        }
}
